Internet Engineering Task Force fge. Galiegue, Ed.
Internet-Draft
Intended status: Informational K. Zyp
Expires: August 5, 2013 SitePen (USA)
G. Court
February 1, 2013
JSON Schema: interactive and non interactive validationdraft-fge-json-schema-validation-00
Abstract
JSON Schema (application/schema+json) has several purposes, one of
which is instance validation. The validation process may be
interactive or non interactive. For instance, applications may use
JSON Schema to build a user interface enabling interactive content
generation in addition to user input checking, or validate data
retrieved from various sources. This specification describes schema
keywords dedicated to validation purposes.
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 5, 2013.
Copyright Notice
Copyright (c) 2013 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
(http://trustee.ietf.org/license-info) in effect on the date of
publication of this document. Please review these documents
carefully, as they describe your rights and restrictions with respect
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Internet-Draft JSON Schema February 20131. Introduction
JSON Schema can be used to require that a given JSON document (an
instance) satisfies a certain number of criteria. These criteria are
materialized by a set of keywords which are described in this
specification. In addition, a set of keywords is defined to assist
in interactive instance generation. Those are also described in this
specification.
This specification will use the terminology defined by the JSON
Schema core specification. It is advised that readers have a copy of
this specification.
2. Conventions and Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
This specification uses the term "container instance" to refer to
both array and object instances. It uses the term "children
instances" to refer to array elements or object member values.
This specification uses the term "property set" to refer to the set
of an object's member names; for instance, the property set of JSON
Object { "a": 1, "b": 2 } is [ "a", "b" ].
Elements in an array value are said to be unique if no two elements
of this array are equal, as defined by the core specification.
3. Interoperability considerations3.1. Validation of string instances
It should be noted that the nul character (\x00) is valid in a JSON
string. An instance to validate may contain a string value with this
character, regardless of the ability of the underlying programming
language to deal with such data.
3.2. Validation of numeric instances
The JSON specification does not define any bounds to the scale or
precision of numeric values. JSON Schema does not define any such
bounds either. This means that numeric instances processed by JSON
Schema can be arbitrarily large and/or have an arbitrarily large
decimal part, regardless of the ability of the underlying programming
language to deal with such data.
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Internet-Draft JSON Schema February 20133.3. Regular expressions
Two validation keywords, "pattern" and "patternProperties", use
regular expressions to express constraints. These regular
expressions SHOULD be valid according to the ECMA 262 [ecma262]
regular expression dialect.
Furthermore, given the high disparity in regular expression
constructs support, schema authors SHOULD limit themselves to the
following regular expression tokens:
individual Unicode characters, as defined by the JSON
specification [RFC4627];
simple character classes ([abc]), range character classes ([a-z]);
complemented character classes ([^abc], [^a-z]);
simple quantifiers: "+" (one or more), "*" (zero or more), "?"
(zero or one), and their lazy versions ("+?", "*?", "??");
range quantifiers: "{x}" (exactly x occurrences), "{x,y}" (at
least x, at most y, occurrences), {x,} (x occurrences or more),
and their lazy versions;
the beginning-of-input ("^") and end-of-input ("$") anchors;
simple grouping ("(...)") and alternation ("|").
Finally, implementations MUST NOT consider that regular expressions
are anchored, neither at the beginning nor at the end. This means,
for instance, that "es" matches "expression".
4. General validation considerations4.1. Keywords and instance primitive types
Some validation keywords only apply to one or more primitive types.
When the primitive type of the instance cannot be validated by a
given keyword, validation for this keyword and instance SHOULD
succeed.
This specification groups keywords in different sections, according
to the primitive type, or types, these keywords validate. Note that
some keywords validate all instance types.
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Internet-Draft JSON Schema February 20134.2. Inter-dependent keywords
In order to validate an instance, some keywords are influenced by the
presence (or absence) of other keywords. In this case, all these
keywords will be grouped in the same section.
4.3. Default values for missing keywords
Some keywords, if absent, MAY be regarded by implementations as
having a default value. In this case, the default value will be
mentioned.
4.4. Validation of container instances
Keywords with the possibility to validate container instances (arrays
or objects) only validate the instances themselves and not their
children (array items or object properties). Some of these keywords
do, however, contain information which is necessary for calculating
which schema(s) a child must be valid against. The algorithms to
calculate a child instance's relevant schema(s) are explained in a
separate section.
It should be noted that while an array element will only have to
validate against one schema, object member values may have to
validate against more than one schema.
5. Validation keywords sorted by instance types5.1. Validation keywords for numeric instances (number and integer)5.1.1. multipleOf5.1.1.1. Valid values
The value of "multipleOf" MUST be a JSON number. This number MUST be
strictly greater than 0.
5.1.1.2. Conditions for successful validation
A numeric instance is valid against "multipleOf" if the result of the
division of the instance by this keyword's value is an integer.
5.1.2. maximum and exclusiveMaximum5.1.2.1. Valid values
The value of "maximum" MUST be a JSON number. The value of
"exclusiveMaximum" MUST be a boolean.
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Internet-Draft JSON Schema February 2013
If "exclusiveMaximum" is present, "maximum" MUST also be present.
5.1.2.2. Conditions for successful validation
Successful validation depends on the presence and value of
"exclusiveMaximum":
if "exclusiveMaximum" is not present, or has boolean value false,
then the instance is valid if it is lower than, or equal to, the
value of "maximum";
if "exclusiveMaximum" has boolean value true, the instance is
valid if it is strictly lower than the value of "maximum".
5.1.2.3. Default value
"exclusiveMaximum", if absent, may be considered as being present
with boolean value false.
5.1.3. minimum and exclusiveMinimum5.1.3.1. Valid values
The value of "minimum" MUST be a JSON number. The value of
"exclusiveMinimum" MUST be a boolean.
If "exclusiveMinimum" is present, "minimum" MUST also be present.
5.1.3.2. Conditions for successful validation
Successful validation depends on the presence and value of
"exclusiveMinimum":
if "exclusiveMinimum" is not present, or has boolean value false,
then the instance is valid if it is greater than, or equal to, the
value of "minimum";
if "exclusiveMinimum" is present and has boolean value true, the
instance is valid if it is strictly greater than the value of
"minimum".
5.1.3.3. Default value
"exclusiveMinimum", if absent, may be considered as being present
with boolean value false.
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Internet-Draft JSON Schema February 20135.2. Validation keywords for strings5.2.1. maxLength5.2.1.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.2.1.2. Conditions for successful validation
A string instance is valid against this keyword if its length is less
than, or equal to, the value of this keyword.
The length of a string instance is defined as the number of its
characters as defined by RFC 4627 [RFC4627].
5.2.2. minLength5.2.2.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.2.2.2. Conditions for successful validation
A string instance is valid against this keyword if its length is
greater than, or equal to, the value of this keyword.
The length of a string instance is defined as the number of its
characters as defined by RFC 4627 [RFC4627].
5.2.2.3. Default value
"minLength", if absent, may be considered as being present with
integer value 0.
5.2.3. pattern5.2.3.1. Valid values
The value of this keyword MUST be a string. This string SHOULD be a
valid regular expression, according to the ECMA 262 regular
expression dialect.
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Internet-Draft JSON Schema February 20135.2.3.2. Conditions for successful validation
A string instance is considered valid if the regular expression
matches the instance successfully. Recall: regular expressions are
not implicitly anchored.
5.3. Validation keywords for arrays5.3.1. additionalItems and items5.3.1.1. Valid values
The value of "additionalItems" MUST be either a boolean or an object.
If it is an object, this object MUST be a valid JSON Schema.
The value of "items" MUST be either an object or an array. If it is
an object, this object MUST be a valid JSON Schema. If it is an
array, items of this array MUST be objects, and each of these objects
MUST be a valid JSON Schema.
5.3.1.2. Conditions for successful validation
Successful validation of an array instance with regards to these two
keywords is determined as follows:
if "items" is not present, or its value is an object, validation
of the instance always succeeds, regardless of the value of
"additionalItems";
if the value of "additionalItems" is boolean value true or an
object, validation of the instance always succeeds;
if the value of "additionalItems" is boolean value false and the
value of "items" is an array, the instance is valid if its size is
less than, or equal to, the size of "items".
5.3.1.3. Example
The following example covers the case where "additionalItems" has
boolean value false and "items" is an array, since this is the only
situation under which an instance may fail to validate successfully.
This is an example schema:
{
"items": [ {}, {}, {} ],
"additionalItems": false
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Internet-Draft JSON Schema February 2013
}
With this schema, the following instances are valid:
[] (an empty array),
[ [ 1, 2, 3, 4 ], [ 5, 6, 7, 8 ] ],
[ 1, 2, 3 ];
the following instances are invalid:
[ 1, 2, 3, 4 ],
[ null, { "a": "b" }, true, 31.000002020013 ]
5.3.1.4. Default values
If either keyword is absent, it may be considered present with an
empty schema.
5.3.2. maxItems5.3.2.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.3.2.2. Conditions for successful validation
An array instance is valid against "maxItems" if its size is less
than, or equal to, the value of this keyword.
5.3.3. minItems5.3.3.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.3.3.2. Conditions for successful validation
An array instance is valid against "minItems" if its size is greater
than, or equal to, the value of this keyword.
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Internet-Draft JSON Schema February 20135.3.3.3. Default value
If this keyword is not present, it may be considered present with a
value of 0.
5.3.4. uniqueItems5.3.4.1. Valid values
The value of this keyword MUST be a boolean.
5.3.4.2. Conditions for successful validation
If this keyword has boolean value false, the instance validates
successfully. If it has boolean value true, the instance validates
successfully if all of its elements are unique.
5.3.4.3. Default value
If not present, this keyword may be considered present with boolean
value false.
5.4. Validation keywords for objects5.4.1. maxProperties5.4.1.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.4.1.2. Conditions for successful validation
An object instance is valid against "maxProperties" if its number of
properties is less than, or equal to, the value of this keyword.
5.4.2. minProperties5.4.2.1. Valid values
The value of this keyword MUST be an integer. This integer MUST be
greater than, or equal to, 0.
5.4.2.2. Conditions for successful validation
An object instance is valid against "minProperties" if its number of
properties is greater than, or equal to, the value of this keyword.
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Internet-Draft JSON Schema February 20135.4.2.3. Default value
If this keyword is not present, it may be considered present with a
value of 0.
5.4.3. required5.4.3.1. Valid values
The value of this keyword MUST be an array. This array MUST have at
least one element. Elements of this array MUST be strings, and MUST
be unique.
5.4.3.2. Conditions for successful validation
An object instance is valid against this keyword if its property set
contains all elements in this keyword's array value.
5.4.4. additionalProperties, properties and patternProperties5.4.4.1. Valid values
The value of "additionalProperties" MUST be a boolean or an object.
If it is an object, it MUST also be a valid JSON Schema.
The value of "properties" MUST be an object. Each value of this
object MUST be an object, and each object MUST be a valid JSON
Schema.
The value of "patternProperties" MUST be an object. Each property
name of this object SHOULD be a valid regular expression, according
to the ECMA 262 regular expression dialect. Each property value of
this object MUST be an object, and each object MUST be a valid JSON
Schema.
5.4.4.2. Conditions for successful validation
Successful validation of an object instance against these three
keywords depends on the value of "additionalProperties":
if its value is boolean true or a schema, validation succeeds;
if its value is boolean false, the algorithm to determine
validation success is described below.
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Internet-Draft JSON Schema February 20135.4.4.3. Default values
If either "properties" or "patternProperties" are absent, they can be
considered present with an empty object as a value.
If "additionalProperties" is absent, it may be considered present
with an empty schema as a value.
5.4.4.4. If "additionalProperties" has boolean value false
In this case, validation of the instance depends on the property set
of "properties" and "patternProperties". In this section, the
property names of "patternProperties" will be called regexes for
convenience.
The first step is to collect the following sets:
s The property set of the instance to validate.
p The property set from "properties".
pp The property set from "patternProperties".
Having collected these three sets, the process is as follows:
remove from "s" all elements of "p", if any;
for each regex in "pp", remove all elements of "s" which this
regex matches.
Validation of the instance succeeds if, after these two steps, set
"s" is empty.
5.4.4.5. Example
This schema will be used as an example:
{
"properties": {
"p1": {}
},
"patternProperties": {
"p": {},
"[0-9]": {}
},
"additionalProperties": false
}
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Internet-Draft JSON Schema February 2013
This is the instance to validate:
{
"p1": true,
"p2": null,
"a32&o": "foobar",
"": [],
"fiddle": 42,
"apple": "pie"
}
The three property sets are:
s [ "p1", "p2", "a32&o", "", "fiddle", "apple" ]
p [ "p1" ]
pp [ "p", "[0-9]" ]
Applying the two steps of the algorithm:
after the first step, "p1" is removed from "s";
after the second step, "p2" (matched by "p"), "a32&o" (matched by
"[0-9]") and "apple" (matched by "p") are removed from "s".
The set "s" still contains two elements, "" and "fiddle". Validation
therefore fails.
5.4.5. dependencies5.4.5.1. Valid values
This keyword's value MUST be an object. Each value of this object
MUST be either an object or an array.
If the value is an object, it MUST be a valid JSON Schema. This is
called a schema dependency.
If the value is an array, it MUST have at least one element. Each
element MUST be a string, and elements in the array MUST be unique.
This is called a property dependency.
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Internet-Draft JSON Schema February 20135.4.5.2. Conditions for successful validation5.4.5.2.1. Schema dependencies
For all (name, schema) pair of schema dependencies, if the instance
has a property by this name, then it must also validate successfully
against the schema.
Note that this is the instance itself which must validate
successfully, not the value associated with the property name.
5.4.5.2.2. Property dependencies
For each (name, propertyset) pair of property dependencies, if the
instance has a property by this name, then it must also have
properties with the same names as propertyset.
5.5. Validation keywords for any instance type5.5.1. enum5.5.1.1. Valid values
The value of this keyword MUST be an array. This array MUST have at
least one element. Elements in the array MUST be unique.
Elements in the array MAY be of any type, including null.
5.5.1.2. Conditions for successful validation
An instance validates successfully against this keyword if its value
is equal to one of the elements in this keyword's array value.
5.5.2. type5.5.2.1. Valid values
The value of this keyword MUST be either a string or an array. If it
is an array, elements of the array MUST be strings and MUST be
unique.
String values MUST be one of the seven primitive types defined by the
core specification.
5.5.2.2. Conditions for successful validation
An instance matches successfully if its primitive type is one of the
types defined by keyword. Recall: "number" includes "integer".
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Internet-Draft JSON Schema February 20135.5.3. allOf5.5.3.1. Valid values
This keyword's value MUST be an array. This array MUST have at least
one element.
Elements of the array MUST be objects. Each object MUST be a valid
JSON Schema.
5.5.3.2. Conditions for successful validation
An instance validates successfully against this keyword if it
validates successfully against all schemas defined by this keyword's
value.
5.5.4. anyOf5.5.4.1. Valid values
This keyword's value MUST be an array. This array MUST have at least
one element.
Elements of the array MUST be objects. Each object MUST be a valid
JSON Schema.
5.5.4.2. Conditions for successful validation
An instance validates successfully against this keyword if it
validates successfully against at least one schema defined by this
keyword's value.
5.5.5. oneOf5.5.5.1. Valid values
This keyword's value MUST be an array. This array MUST have at least
one element.
Elements of the array MUST be objects. Each object MUST be a valid
JSON Schema.
5.5.5.2. Conditions for successful validation
An instance validates successfully against this keyword if it
validates successfully against exactly one schema defined by this
keyword's value.
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Internet-Draft JSON Schema February 20135.5.6. not5.5.6.1. Valid values
This keyword's value MUST be an object. This object MUST be a valid
JSON Schema.
5.5.6.2. Conditions for successful validation
An instance is valid against this keyword if it fails to validate
successfully against the schema defined by this keyword.
5.5.7. definitions5.5.7.1. Valid values
This keyword's value MUST be an object. Each member value of this
object MUST be a valid JSON Schema.
5.5.7.2. Conditions for successful validation
This keyword plays no role in validation per se. Its role is to
provide a standardized location for schema authors to inline JSON
Schemas into a more general schema.
As an example, here is a schema describing an array of positive
integers, where the positive integer constraint is a subschema in
"definitions":
{
"type": "array",
"items": { "$ref": "#/definitions/positiveInteger" },
"definitions": {
"positiveInteger": {
"type": "integer",
"minimum": 0,
"exclusiveMinimum": true
}
}
}
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Internet-Draft JSON Schema February 20136.1. "title" and "description"6.1.1. Valid values
The value of both of these keywords MUST be a string.
6.1.2. Purpose
Both of these keywords can be used to decorate a user interface with
information about the data produced by this user interface. A title
will preferrably be short, whereas a description will provide
explanation about the purpose of the instance described by this
schema.
Both of these keywords MAY be used in root schemas, and in any
subschemas.
6.2. "default"6.2.1. Valid values
There are no restrictions placed on the value of this keyword.
6.2.2. Purpose
This keyword can be used to supply a default JSON value associated
with a particular schema. It is RECOMMENDED that a default value be
valid against the associated schema.
This keyword MAY be used in root schemas, and in any subschemas.
7. Semantic validation with "format"7.1. Foreword
Structural validation alone may be insufficient to validate that an
instance meets all the requirements of an application. The "format"
keyword is defined to allow interoperable semantic validation for a
fixed subset of values which are accurately described by
authoritative resources, be they RFCs or other external
specifications.
The value of this keyword is called a format attribute. It MUST be a
string. A format attribute can generally only validate a given set
of instance types. If the type of the instance to validate is not in
this set, validation for this format attribute and instance SHOULD
succeed.
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Internet-Draft JSON Schema February 20137.2. Implementation requirements
Implementations MAY support the "format" keyword. Should they choose
to do so:
they SHOULD implement validation for attributes defined below;
they SHOULD offer an option to disable validation for this
keyword.
Implementations MAY add custom format attributes. Save for agreement
between parties, schema authors SHALL NOT expect a peer
implementation to support this keyword and/or custom format
attributes.
7.3. Defined attributes7.3.1. date-time7.3.1.1. Applicability
This attribute applies to string instances.
7.3.1.2. Validation
A string instance is valid against this attribute if it is a valid
date representation as defined by RFC 3339, section 5.6 [RFC3339].
7.3.2. email7.3.2.1. Applicability
This attribute applies to string instances.
7.3.2.2. Validation
A string instance is valid against this attribute if it is a valid
Internet email address as defined by RFC 5322, section 3.4.1
[RFC5322].
7.3.3. hostname7.3.3.1. Applicability
This attribute applies to string instances.
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Internet-Draft JSON Schema February 20137.3.3.2. Validation
A string instance is valid against this attribute if it is a valid
representation for an Internet host name, as defined by RFC 1034,
section 3.1 [RFC1034].
7.3.4. ipv47.3.4.1. Applicability
This attribute applies to string instances.
7.3.4.2. Validation
A string instance is valid against this attribute if it is a valid
representation of an IPv4 address according to the "dotted-quad" ABNF
syntax as defined in RFC 2673, section 3.2 [RFC2673].
7.3.5. ipv67.3.5.1. Applicability
This attribute applies to string instances.
7.3.5.2. Validation
A string instance is valid against this attribute if it is a valid
representation of an IPv6 address as defined in RFC 2373, section 2.2
[RFC2373].
7.3.6. uri7.3.6.1. Applicability
This attribute applies to string instances.
7.3.6.2. Validation
A string instance is valid against this attribute if it is a valid
URI, according to [RFC3986].
8. Reference algorithms for calculating children schemas8.1. Foreword
Calculating the schema, or schemas, a child instance must validate
against is influenced by the following:
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the container instance type;
the child instance's defining characteristic in the container
instance;
the value of keywords implied in the calculation.
In addition, it is important that if one or more keyword(s) implied
in the calculation are not defined, they be considered present with
their default value, which will be recalled in this section.
8.2. Array elements8.2.1. Defining characteristic
The defining characteristic of the child instance is its index within
the array. Recall: array indices start at 0.
8.2.2. Implied keywords and default values.
The two implied keywords in this calculation are "items" and
"additionalItems".
If either keyword is absent, it is considered present with an empty
schema as a value. In addition, boolean value true for
"additionalItems" is considered equivalent to an empty schema.
8.2.3. Calculation8.2.3.1. If "items" is a schema
If items is a schema, then the child instance must be valid against
this schema, regardless of its index, and regardless of the value of
"additionalItems".
8.2.3.2. If "items" is an array
In this situation, the schema depends on the index:
if the index is less than, or equal to, the size of "items", the
child instance must be valid against the corresponding schema in
the "items" array;
otherwise, it must be valid against the schema defined by
"additionalItems".
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Internet-Draft JSON Schema February 20138.3. Object members8.3.1. Defining characteristic
The defining characteristic is the property name of the child.
8.3.2. Implied keywords
The three keywords implied in this calculation are "properties",
"patternProperties" and "additionalProperties".
If "properties" or "patternProperties" are absent, they are
considered present with an empty object as a value.
If "additionalProperties" is absent, it is considered present with an
empty schema as a value. In addition, boolean value true is
considered equivalent to an empty schema.
8.3.3. Calculation8.3.3.1. Names used in this calculation
The calculation below uses the following names:
m The property name of the child.
p The property set from "properties".
pp The property set from "patternProperties". Elements of this set
will be called regexes for convenience.
s The set of schemas for the child instance.
8.3.3.2. First step: schemas in "properties"
If set "p" contains value "m", then the corresponding schema in
"properties" is added to "s".
8.3.3.3. Second step: schemas in "patternProperties"
For each regex in "pp", if it matches "m" successfully, the
corresponding schema in "patternProperties" is added to "s".
8.3.3.4. Third step: "additionalProperties"
The schema defined by "additionalProperties" is added to "s" if and
only if, at this stage, "s" is empty.
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